One of the probabilistic safety targets established for NPP by Regulatory body is the annual probability of big radioactive release. At seismic and other external loadings this probability depends on annual probability of seismic loads of different levels, on conditional probability of rupture of piping of reactor facility in the case of realization of seismic load of some level and of conditional probability of damage of containment in the case of rupture of reactor facility piping. Achievement the strength criterion by stress in critical point of containment is considered as a damage of containment. Considering this fact, probabilistic evaluations of this criterion was defined in the terms of numbers of standard deviations from mathematical expectation of strength for different levels of external load and different probabilities of rupture of reactor facility piping. As a result was obtained that to correspond with safety target it is necessary to use for the same material as bigger strength margin, the bigger is annual probability of considered level of external action and the bigger is the probability of rupture of reactor facility piping. This function was numerically demonstrated for concrete used for real containment of reactor
